In packaging technique packages of the non-returnable type have been in use for a long time which are manufactured from a material which consists of a carrier layer of cardboard or paper and outer and inner coatings of thermoplastics. Frequently the packing material in such packages is also provided with additional layers of other material, e.g. aluminum foil or plastic layers other than those mentioned.
The composition of the packing material is intended to create the optimum product protection for the goods which are to be packed, and to impart sufficient mechanical protection for the product in the package and adapting it so that it can be readily handled by the user of the package. In order to achieve mechanical rigidity sufficient to provide mechanical protection for the contents and to make it possible for the package to be handled and gripped by hand without difficulty, the packages of this type are often provided with a carrier layer of paper or cardboard which gives the package rigidity of form and affords mechanical protection. Such a carrier layer, however, is permeable to gases or liquids and the rigidity of the material disappears if the material is subjected to moisture or if liquid is absorbed into the material. To make the material satisfactorily impermeable to liquids, it is most frequently laminated with a plastic material, and if this plastic material is thermoplastic, the plastic layers can be sealed to each other with the help of heat and pressure. In this manner, the packaging container can be sealed and given permanent form by the sealing of the plastic coated material panels to each other in a tight and mechanically durable and strong seal.
Packing containers of the type referred to here are manufactured either from blanks punched out beforehand or from a continuous web which has been prepared with suitable decoration and with a crease line pattern for facilitating its folding. The packing containers are manufactured from such a web by joining together the longitudinal edges of the web in an overlap join so as to form a tube which is subsequently filled with the intended contents and divided into closed container units by repeated transverse sealing of the tube perpendicularly to the longitudinal axis of the tube. After suitable folding of the packing material in the tube the material in the said container units is converted to the desired geometrical shape, usually a parallelepiped, by providing the tube with longitudinal folding lines and with double-walled triangular lugs at the corners of the packing container.
Whether the packing containers are manufactured from blanks produced beforehand or from a continuous web, the material, for practical reasons, will be of uniform thickness. This means that the material, and in particular the carrier layer of paper or cardboard, is mechanically overstrong or overdimensioned along certain regions which during normal use and handling are not subjected to more substantial mechanical stresses whilst other parts of the material in the package ought to be thicker or more rigid in order to withstand the mechanical strains which they are subjected to. In other words it would be desirable for the material to be of differential thickness so as to allow optimum economic utilization of the material.